FIG. 1 shows the basic structure of a human eye 1 which comprises a cornea 3, a pupil 5, a lens 7, and a retina 9. The retina 9 is an internal light sensitive layer at the back of the eye 1 and is primarily responsible for vision. Light from a distant object or light source 11 travelling in a near parallel path enters the eye through the pupil 5 and is focused at a point on the retina 9 by the refractive power of the cornea 3 and lens 7. The light focussed on the retina 9 is detected by photoreceptor cells of the retina 9, and converted into an electrical signal. The electrical signal is transferred by retinal ganglion cells, through the optic nerve of the eye 1, into the brain for visual processing. This is generally how a human can see the outside world.
Unlike the cornea 3, the retina 9 is currently not replaceable. Currently there is no artificial retina or other substitutes that can provide sufficient visual function in the event the retina fails. Unfortunately, the retina 9 is quite vulnerable to various problems and diseases and is therefore subject to failure. Consequently, care should be taken to ensure the health of the retina. Furthermore, since the retina is the only portion of the central nervous system visible from outside the human body, inspection of the retina can enable detection of other health issues such as diabetes. Therefore, examination of the retina 9 is one of the most important aspects of an eye examination because it enables the detection and prevention of pathological conditions that can result in irreversible visual loss or other health related issues.
An eye examination is traditionally carried out by a specialist eye doctor, commonly referred to as an ophthalmologist, who visually inspects the fundus of the eye using an ophthalmoscope. One limitation of an ophthalmoscope is that it is unable to contemporaneously record visual details of the fundus which means that the ophthalmologist is required to subsequently document his findings of the visual inspection of the retina in text or drawings. Accurate recording or documentation of images of the fundus require another instrument commonly referred to as a retinal camera or fundus camera. The process of taking photographs of the retina is called fundus photography. Fundus photography provides photographic documentation of the retina and facilitates documentation, monitoring, case discussion, mass screening, and even telemedicine.
Conventional fundus cameras are usually large machines that must be table mounted and connected to a desktop computer system for image storage and organisation. Such conventional cameras are not helpful for bed-bound patients, infants and children, or other patients that cannot easily move or cooperate for accurate positioning relative to the camera. Furthermore, such cameras limit the examination to the clinic or hospital. Outreach screening with such fundus cameras is therefore very difficult.
Recently, a number of portable fundus cameras have been developed to address these mobility issues. These portable fundus cameras have greatly expanded the ability to conduct funduscopic or ophthalmoscopic examinations. However, portable fundus cameras still require relatively complicated connection to a computer system for photo storage, processing and organisation. Auto-analysis and telemedicine is possible with such cameras, but is still limited to specialist centres that have the dedicated facilities and computer systems for assessment.
With the advent of smartphones and other portable image acquisition devices, retinal imaging with smartphones is gaining popularity. One advantage of using a smartphone for retinal imaging is that it does not require connection to remote computer systems. Smartphones also allow instant image capture, review, analysis, organisation and sharing of fundus photographs. As smartphones are popular among health care professionals, every suitably qualified health care professional with a smartphone and an appropriate adaptor has the necessary technology to perform fundus photography.
Apart from the ease of use, there are many additional advantages of using a smartphone and adaptor to take photographs of the fundus. With constant improvements in smartphone camera technology, the resolution of fundus photographs will correspondingly improve. Various smartphone software can also be developed by third parties to further improve diagnostic performance and facilitate patient care. As modern smartphone cameras can offer high light sensitivity, smartphones can be used to take fundus photographs under lower illumination levels than traditional ophthalmoscopy apparatus.
There are a number of such adaptors on the market. However, most of them offer a limited field of view (at most around 50 degrees of view). This limited field of view can only show the central part of the retina. In order to provide a more comprehensive screening of the retina, a much wider field of view is needed. On the other hand, the adaptor should be small and lightweight to facilitate portable clinical use.
It is an object of the present invention to provide an improved adaptor for a portable image acquisition device for fundus photography with a wider field of view.